1. Field of the Invention
This invention relates to an improved method and apparatus for maintaining and dressing commutators and slip rings of large industrial motors, generators, convertors and similar machinery, with or without removal of the armature from the machine.
2. Description of the Prior Art
It is known in the art to traverse either a fixed grinding stone or a grinding wheel across the face of a commutator or slip ring of an armature while the armature remains in its normal bearings and spins in the bearings while the surface is dressed. Several patents have employed grinding wheels driven by belts from remote motors, such as Chappell U.S. Pat. No. 1,072,410 and Mauran U.S. Pat. No. 1,446,982. Chappell described his main shaft as rotating at a "very high speed" of between 1,800 and 2,500 rpm.
Also representative of the prior art is a Westinghouse Maintenance Bulletin, ESDL No. 50-27, Supp. 2 which recommends trueing tool steel collector rings with a precision rotating grinder mounted on a lathe carriage, using an 80 or 120 grit wheel spinning to produce a 3,500 to 4,500 feet per minute (1050 to 1400 meters per minute) surface speed. This Bulletin specifies that only one-fourth inch of the wheel width should be in contact with the collector ring during grinding. For larger, higher-speed collector rings on turbine generators, rotational speeds of 3,900 to 5,650 feet (1,200 to 1,700 meters) per minute and use of 1-inch (2.54 cm) thick wheels of 80 to 120 grit are recommended. The Westinghouse Bulletin cautions that the spiral groove in the ring should be rechamfered after grinding to remove burrs caused by the wheel dragging the ring material over or into the groove.